(1) Field of the Invention
This invention relates to acoustic detection systems for detecting acoustic signals. More particularly, the present invention relates to acoustic systems which are employed in undersea applications for detecting acoustic pressure pulses from various underwater sources.
(2) Description of the Prior Art
Conventional acoustic detection systems to which this invention relates employ linear acoustic receiving arrays of discrete acoustic sensors or hydrophone elements, which are spaced at intervals along the array. In some systems a large number of hydrophones may be employed and electrically connected through a platform where the various signal processing and output equipment are located. Conventional sonar systems employ magneto-strictive or ceramic elements which are relatively expensive and cumbersome. Such conventional acoustic systems may employ acoustic line array configurations which are either towed behind a vessel or disposed in a fixed relationship.
In U.S. Pat. No. 4,176,339 entitled "Propagation Sampled Acoustic Line Array", an acoustic line array includes a co-axial cable having a central conductor surrounded by a flexible material of low-electrical conductivity. The flexible material is surrounded by a conducting material protected by an external shield. A characteristic impedance of the cable is sensitive to pressure variations in the surrounding medium due to traveling acoustic pressure waves from an acoustic source. The acoustic source is detected by use of reflectometry techniques and by variations in the impedance of the array. In one embodiment, the line array employs discrete sensors which are located at suitable intervals along the array. A sample pulse generator is coupled to one end of the cable. The cable terminates in characteristic impedance. It is desirable to use this principle for an acoustic transducer system.